1. Field of the Invention
The present invention relates to a channel bonding receiving apparatus and method for expanding a channel bonding receiving band in a cable modem; and more particularly, to a channel bonding receiving apparatus and method for expanding a channel bonding receiving band, which expands a receiving band range (i.e., a channel bonding receiving band range) capable of receiving a broadband signal containing a channel bonding signal and thus can support a free channel bonding arrangement in a transmitting side.
This work was supported by the IT R&D program of MIC/IITA [2006-S-019-02, “The Development of Digital Cable Transmission and Receive System for 1 Gbps Downstream”].
2. Description of Related Art
Data Over Cable Service Interface Specification (DOCSIS) 3.0 is a technology that provides an Internet speed of above 150 Mbps for downlink and above 120 Mbps for uplink in a hybrid fiber-coaxial (HFC) network. The DOCSIS 3.0 physical layer specification was issued by CableLabs in August 2006 and recently updated in February 2008.
The DOCSIS 3.0 uses a channel bonding technique that transmits a number of 6-MHz band signals in a binding manner. Unlike the pre-existing DOCSIS 2.0, the DOCSIS 3.0 requires a complicated media access control (MAC) technique and a technique for a physical layer (PHY) including a radio frequency (RF) tuner and a digital demodulator, in order for a receiving terminal support the channel bonding technique.
A cable modem for up to the DOCSIS 2.0 receives a 54˜864 MHz band signal from an HFC network, down-converts the 54˜864 MHz band signal into an intermediate frequency (IF) signal (generally 44 MHz) by means of an RF tuner, and digital-demodulates the dunned 6-MHz band signal.
However, from the DOCSIS 3.0, a PHY section simultaneously receives signals obtained by bonding four or more channels, digitizes the received signals, and hands the resulting signals to a MAC module. To this end, as illustrated in FIG. 1, a PHY section of a conventional DOCSIS 3.0 cable modem includes: a broadband RF tuner 101 for tuning a broadband signal; an analog-to-digital (A/D) converter 102 for converting an analog signal into a digital signal; a digital channelizer 103 for selecting (or extracting) only a bonded channel from a tuned band; and a demodulator unit 11 including four or more demodulators.
If an MT2170 DOCSIS 3.0 broadband tuner, which was issued by Microtune Inc. in March 2007, is used as the broadband RF tuner 101, a DOCSIS 3.0 bonding channel receiving structure illustrated in FIG. 1 can receive a channel bonded within an up to 100-MHz band.
However, when considering the fact that a DOCSIS 3.0 downlink frequency band is of 101˜876 MHz, the restriction that channel bonding can be supported only within a 100-MHz band increases the inflexibility in a system operation such as load balancing.
For example, in case of using an MT2170 tuner as the broadband RF tuner 101, if a system operator locates one bonding channel at 500 MHz, other bonding channels must be located in a 400˜500-MHz band or a 500˜600-MHz band. In this case, if other bonding channels are located at 300 MHz, a difference with a 500-MHz band exceeds 100 MHz, thus making it impossible for the cable modem to receive all the bonding channels.
As described above, since a receiving band range (i.e., a channel bonding receiving band range) capable of receiving a broadband signal (e.g., a cable signal transmitted through an HFC network) containing a channel bonding signal is narrow and restricted, the conventional channel bonding receiving technology cannot support a free channel bonding arrangement in a transmitting side.